Dryer control



April 1969 s. H. FATHAUER 3,439,991

I DRYER CONTROL Filed Jan. 20, 1967 Fig.1

INVENTOR. Geo/ye fiK/Z/fiaaer WATTORNEYS BYv United States Patent F us. (:1. 431-41 19 Claims ABSTRACT OF THE DISCLOSURE A control circuit for a burner employing an oscillator having a fixed operating time, a transformer connected to an output of the oscillator to produce a high voltage discharge across a pair of igniter electrodes, a fuel valve actuator connected to an output of the oscillator, and a thermistor connected between a source of voltage and the fuel valve actuator. The thermistor is dimensioned to provide holding current only for the fuel valve actuator after it has been initially actuated by the oscillator output and only if the temperature of the burner is sufiiciently high at the termination of the output signal from the oscillator.

Background of the invention Field of the invention.This invention relates generally to a burner control circuit and more particularly to a circuit for simultaneously controlling the ignition of fuel within a burner and the flow of fuel thereto, and subsequently either maintaining or discontinuing the flow of fuel depending upon the temperature conditions within the burner. The present invention has specific application in a gas dryer machine.

Description of the prior art.Burner controls are relatively old in the art, per se, including those of the electrical or electronic type. However, some of the prior art control devices employ a separate circuit for the igniter and a separate and independent circuit for controlling the fuel valve. For instance, many of such prior art controls employ a manually operable switch which must be depressed for a predetermined time, during which time the igniter is operated and the fuel valve is actuated. In those circuits, the fuel valve is usually controlled after initial actuation thereof by the manually operable switch in response to a temperature within the burner. However, initial actuation of the fuel valve is not automatic and is entirely within the control of an operator.

In those circuits which require the manual actuation of a switch by an operator, in order to provide a completely hazardous free operation, a timer must be employed with the manually operable switch so that only a metered amount of fuel will be supplied to the burner. Without such a timer, an operator may continue to supply fuel to the burner by maintaining the manually operable switch closed. It is therefore possible, without a timer in circuit with the switch, to deliver a greater quantity of fuelto the burner than that desired and to produce a hazardous condition thereby. The provision of separate circuits for the igniter and the fuel valve of a burner and the requirement of a timer, of course, increases the cost of such burner controls. In addition, in those prior art controls which employ a manually operable switch, an operator must maintain the switch actuated for a predetermined time. As a result, an unsafe condition may be created through neglect of the operator.

3,439,991 Patented Apr. 22, 1969 Summary of the invention It is, therefore, an object of the present invention to provide a burner control circuit which employs a single source of excitation for controlling the ignition of fuel within a burner and for controlling the flow of fuel thereto.

It is another object of the present invention to provide a burner control circuit which simultaneously controls the ignition of a fuel within a burner and the flow of fuel thereto, and subsequently either maintains or discontinues the flow of fuel depending upon the temperature conditions within the burner.

Still another object of the present invention is to provide a burner control circuit which is not dependent upon an operators judgment nor subject to an operators negligence.

Accordingly, the present invention provides a single source of excitation current for an igniter and for a fuel control valve and further provides means responsive to the temperature within the burner for maintaining the fuel valve actuated after it has been initially actuated by the excitation source and only if the tempearture of the burner is sufficiently high.

An important feature of the present invention resides in the provision of a single source of excitation current for controlling the igniter and the fuel valve for a burner, which excitation source has a fixed operating time.

Another important feature of the present invention resides in the provision of a circuit element which is responsive to the temperature of the burner for maintaining the fuel valve actuated after it has been initially actuated by the excitation source and only if the temperature of the burner is sufficiently high.

Brief description of the drawing These and other objects, features and advantages of the present invention will be more fully realized and understood from the following detailed description when taken in conjunction with the accompanying drawing wherein:

FIGURE 1 is a schematic diagram of a control circuit constructed in accordance with the principles of the present invention; and

FIGURE 2 is a diagrammatic view in section of a burner which may be employed in conjunction with the control circuit illustrated in FIGURE 1.

Like reference numerals throughout the various views of the drawing are intended to designate the same or similar structures.

Description of the preferred embodiment With reference to FIGURE 1, there is illustrated a circuit diagram of the control circuit constructed in accordance with the principles of the present invention. As shown therein, a power supply 10 supplies direct current voltage through a switch 12 to the control circuit, generally designated with the reference numeral 14. The switch 12 may be an on-off switch, a thermostat, or any device intended to initiate the operation of a burner.

The control circuit 14 generally includes an excitation source, designated with the reference numeral 16, a high voltage section, generally designated with the reference numeral 18, a fuel valve actuator generally designated with the reference numeral 20, and a fuel valve actuator hold-in circuit, generally designated with the reference numeral 22.

tor includes a pair of transistors 24 and 26 having their emitters connected to the source of direct current voltage and their collectors connected through resistors 28 and 30 respectively to ground potential. The collector of the transistor 24 is coupled to the base of the transistor 26 by a capacitor 32 and the collector of the transistor 26 is coupled to the base of the transistor 24 by a capacitor 34. The base of the transistor 26 is connected to ground potential through a resistor 36 and the base of the transistor 24 is connected through a circuit 38 to ground potential.

In particular, the circuit 38 includes a resistor 40 and a capacitor 42 which are connected in series with one another between the base of the transistor 24 and ground potential. A junction between the resistor 40 and the capacitor 42 is connected to the DC voltage source through a diode 44. In addition, a capacitor 45 is connected in parallel to the resistor 40. The capacitor 32, the capacitor 34, the resistor 36, the capacitor 45, and circuit 38 determine the period of oscillation of the multivibrator circuit. However, the circuit 38 is constructed to continually increase the time between successive pulses at an output of the multivibrator.

Upon initial application of the DC source of voltage to the multivibrator or oscillator circuit, a series of pulses will appear at an output thereof. These pulses coupled through the capacitor 34 will develop a charge on the capacitor 42 which will gradaully increase as the multivibrator continues to provide an output. As the charge on the capacitor 42 increases, the time between successive pulses at an output of the multivibrator will also increase until the charge on the capacitor 42 reaches a predetermined level to maintain the transistor 24 nonconductive and cause the oscillatory action on the multivibrator to cease. As a result, the output from the multivibrator will be discontinued when the capacitor 42 has been charged to the required level.

During the time that the DC voltage is applied to the multivibrator through the switching device 12, the diode 44 is back-biased and will not permit the capacitor 42 to discharge. In addition, after the capacitor 42 has been charged to the predetermined level, the transistor 26 is maintained in a conductive state causing the junction point of the capacitor 34 and resistor 30 to be maintained substantially at the level of the DC voltage. This condition will also retain the charge on the capacitor 42 and will not permit it to become discharged. However, when the DC voltage is removed from the multivibrator by opening the switching device 12, the capacitor 42 will 'be discharged through the diode 44. Preferably, the values of the resistor 40 and capacitor 42 are dimensioned to develop the required charge on the capacitor 42 in approximately thirty seconds.

An output of the multivibrator is connected through a resistor 46 and a capacitor 48 in parallel with one another to the base of a transistor 50. The circuit including the resistor 46 and capacitor 48 matches the multivibrator output power to the transistor 50. The transistor 50 performs as a switching device in the circuit. In particular, the emitter of the transistor 50 is connected to the source of direct current voltage through the switching device 12 and the collector thereof is connected to one end of a primary winding 52 of a high voltage transformer 54. A tap of the primary winding 52 is connected to ground potential and the other end thereof is connected through a diode 56 to the fuel valve actuator 20. The transformer 54 includes a secondary winding 58 which is connected on one seide thereof through a capacitor 60' to to a first igniter electrode 62 and on the other side thereof to a second igniter electrode 64. The electrode 64 is connected to ground potential. The igniter electrodes 62 and 64 are disposed in spaced relationship with respect to one another to define a voltage discharge gap 66 therebetween.

When an output is being delivered from the multivibrator, negative-going pulses render the transistor 50 conductive to provide a current fiow from the source of direct current voltage through a portion of the primary winding 52 to ground potential. A positive-going pulse from the multivibrator 16 renders the transistor nonconductive and the resultant rapid decay of current through the primary winding 52 develops a relatively large potential across the secondary winding 58 and a voltage discharge across the gap 66. At the same time, a voltage is developed in a winding portion 52a of the primary winding 52 which supplies a current through the diode rectifier 56 and to the fuel value actuator 20. A capacitor 68 is connected across the fuel valve actuator 20 and performs to filter the alternating current pulses supplied thereto and to develop a substantially direct current voltage across the fuel valve actuator 20. The fuel valve actuator 20 is illustrated in the drawing as a solenoid 70. The capacitor 60 in series with the igniter electrodes 62 and 64 limits the power supplied to the igniter gap 66 so that sufiicient current will be developed in the winding portion 52a to permit the fuel valve actuator 20 to be energized.

A thermistor 72 is connected to the source of direct current voltage and also through a resistor 74 to the fuel valve actuator 20. The thermistor 72 is mounted in heat communication with the burner and is dimensioned to provide hold-in current for the fuel valve actuator 20 after the actuator has been initially energized by the remaining circuitry and only if it is raised to a predetermined temperature. The resistor 74 in series with the thermistor 72 reduces self heating of the thermistor. Preferably, the thermistor 72 must be heated to a temperature of approximately 300 F. before it will conduct sufiicient current to hold the fuel valve actuator 20 energized. However, if the fuel valve actuator 20 is not initially energized, conduction of current through the thermistor 72, regardless of its temperature, will not independently energize the fuel valve actuator 20. Preferably, the time constant circuit of the multivibrator 16 including the resistor 40 and the capacitor 42 is matched to the heating time of the thermistor 72. Therefore, the fuel valve actuator 20 is energized only when the multivibrator 16 is generating an output. Since less current is required to maintain the fuel valve actuator 20 energized, the thermistor 72 will maintain the actuator 20 energized if suflicient heat is reflected thereto.

It can be readily appreciated that the circuit performs the following functions automatically upon closure of the switching device 12:

( 1) Energization of the fuel ignition circuit;

(2) Energization of the fuel valve actuator; and

(3) Maintain the fuel valve actuator energized if ignition has occurred or deenergize the same if proper ignition has not occurred.

FIGURE 2 illustrates a feature of the present invention which permits the use of a less expensive thermistor in the circuit illustrated in FIGURE 1. In particular, a burner housing, generally designated with the reference numeral supports a burner 82 therein which is supplied with fuel from a conduit 84 having a fuel valve 86 therein. The fuel valve 86 is controlled by the fuel valve actuator 20 to control the supply of fuel to the burner 82. The burner housing 80 includes a plurality of air inlets 88 which permit the passage of air to the burner to be heated. The igniter electrodes 62 and 64 are mounted on a wall of the burner housing 80 adjacent the burner 82. In addition, a bypass or a recirculation conduit 90 extends between an opening 92 in an upper portion of the housing 80 and an opening 94 in the lower portion of the housing 80. The thermistor 72 is mounted within the recirculation conduit 90. Heated air passes through the conduit 90 as indicated by the arrows in FIGURE 2 and supplies heat to the thermistor 72 when proper ignition of the fuel has taken place. Consequently, the thermistor 72 may not be located directly in or adjacent the flame and, consequently, .is not subjected to relatively high temperatures. Therefore, a less expensive thermistor can be employed in the circuit illustrated in FIGURE 1.

The circuit illustrated in FIGURE 1 was operated successfully with the circuit elements dimensioned as follows:

The drawings and specification present a detailed disclosure of the preferred embodiments of the invention, and it is to be understood that the invention is not limited to the specific forms disclosed, but covers all modifications, changes and alternative constructions and methods falling within the scope of the principles taught by the inVentiOn.

I claim: y

1. A control circuit for a fuel valve and an igniter of a burner, comprising:

(a) means for producing a control signal of predetermined time duration, said control signal producmg means including a multivibrator having at least one time determining circuit for controlling the time period of successive pulses of said control signal at an output thereof, said time determining circuit including means responsive to the lapsed operating time of said multivibrator for rendering said multivibrator inoperative after said predetermined time duration,

(b) means responsive to said control signal for producing a voltage discharge at the igniter,

(0) means responsive to said control signal for actuating the fuel valve, and

(d) means responsive to a predetermined level of temperature within the burner for maintainlng the fuel valve actuated after initial actuation thereof by said actuating means.

2. A control circuit as defined in claim 1, wherein said voltage discharge producing means includes a transformer having a primary winding connected to an output of said multivibrator and a secondary winding connected to the igniter.

3. A control circuit as defined in claim 1, further comprising meansfor initiating operation of said control signal producing means.

4. A control circuit as defined in claim 1, wherein sa1d rendering means includes a capacitor and means for supplying successive pulses of said control signal to sa1d capacitor for developing a charge thereon proportioned to the number of pulses supplied thereto.

5. A control circuit as defined in claim 4, wherein said multivibrator includes at least one transistor having a base electrode connected to said capacitor.

6. A control circuit as defined in claim 1, wherein said voltage discharge producing means includes a transformer having a primary winding connected to said control signal producing means and a secondary winding connected to the igniter, and wherein said actuating means includes a further winding on said transformer and a solenoid disposed for actuating the fuel valve and connected to said further winding.

7. A control circuit as defined in claim 6, further comprising a rectifier connected in series between said further winding and said solenoid.

8. A control circuit as defined in claim 7, further comprising a capacitor connected across said solenoid.

9. A control circuit as defined in claim 1, wherein said maintaining means includes a thermistor.

10. A control circuit as defined in claim 9, wherein the burner includes a recirculation conduit, and wherein said thermistor is mounted in said recirculation conduit.

11. A control circuit as defined in claim 1, further comprising a source of direct current potential, and wherein said voltage discharge producing means includes a switching device and a transformer having a primary winding and a secondary winding, said switching device being connected for actuation thereof to said control signal producing means and between said source of direct current potential and said primary winding, said secondary winding being connected to the igniter, whereby a voltage discharge results in the ignitor as a result of a rapid decay of current in said primary winding in response to said switching device.

12. In combination with a burner, a valve for supplying fuel to the burner, and igniter electrodes disposed for igniting the fuel at the burner, a control circuit, comprismg:

(a) means for producing a series of pulses for a predetermined time,

(b) means for producing a voltage discharge across the igniter electrodes in response to said series of pulses,

(c) means responsive to the temperature of the burner for developing a control current having a magnitude proportional to the temperature, and

(d) means for actuating the valve in response to said series of pulses and for maintaining the valve actu- =ated only in response to a predetermined magnitude of said control current.

13. In combination with a burner, a valve for supplying fuel to the burner, and igniter electrodes for igniting the fuel at the burner, a control circuit comprising:

(a) a multivibrator having an output in the form of a series of pulses and having circuit means controlling the time duration of said series of pulses,

(b) a transformer having a primary winding connected to said output and a first secondary winding connected to the igniter electrodes,

(c) a fuel valve actuator mechanically connected to the valve, said transformer having a second secondary winding connected to said actuator,

(d) a source of voltage, and

(e) a thermistor disposed in heat communication with the burner and connected between said source of voltage and said actuator.

-14. A combination as defined in claim 13, further comprising a switching device having a switching control element, said output being connected to said control element and said switching device being connected between said source of voltage and said primary Winding.

15. A combination as defined in claim 14, further comprising a rectifier connected between said second secondary winding and said actuator.

16. A combination as defined in claim 15, further comprising a capacitor connected across said actuator.

17. A combination as defined in claim 13, wherein said multivibrator includes a pair of transistors each having an emitter electrode, a collector electrode and a base electrode, a pair of resistors, said emitter electrode and said collector electrode of each of said transistors being connected in series with a respective one of said resistors between said source of voltage and a reference potential, a first capacitor connected between the base of one of said transistors and a junction of one of said resistors with the other of said transistors, a second capacitor connected between the base of said other transistor and a junction of the other of said resistors with said one transistor, 9. third resistor connected between the base of said other transistor and said reference potential, and a fourth resistor and a third capacitor connected in series with one another between the base of said one transistor and said reference potential.

18. A combination as defined in claim 17, further comprising a rectifier connected from a junction of said fourth resistor with said third capacitor to said source of voltage.

19. A combination as defined in claim 18, further comprising a fourth capacitor connected across resistor.

said fourth References Cited UNITED STATES PATENTS 7/1964- Weber et a1. 431-43 8/1967 Walker 431 71 US. Cl. X.R. 

